Auto Tuner

Users Manual

By

Brian Crosby

Topics Page No.

Section 1 General Introduction___________________________2

Greetings____________________________________________________2

Features_____________________________________________________2

Specifications________________________________________________2

Section 2 Installation Instructions____________________3

Getting Started_______________________________________________3

Tuning String________________________________________________3

Step-by-Step Instructions_______________________________________4

Section 3 Theory of operation_______________________5

General Overveiw____________________________________________5

Electrical___________________________________________________6

Software____________________________________________________7

Mechcanical_________________________________________________8

Appendices_________________________________________________9

Section 1 General Introduction

Greetings:

Thank you for purchasing the Auto Tuner product from B.C. Corporation. Your newly purchased Auto Tuner is a state of the art tuner that uses advance technology to tune any six-string acoustic or electric guitar quickly and accurately. No more fighting to find the right tuning for your stings. The Auto Tuner does automatic string-by-string tuning accurately within fractions of seconds, leaving you with the more important things to like your music.

Features:

The Auto Tuner comes with the following features:

>LCD screen display with Visual menu.

>3 different tuning selections for music preference.

>Battery operated for portability.

>Microphone for acoustic and ¼ inch jack for electric inputs.

>Fast smart software that tunes within a pluck of the string.

>Ease touch soft buttons

>Battery save, unit tunes off automatically when not in use.

Specifications:

The Auto Tuner has the following Key Specifications:

Electrical:

>Runs on six AA batteries

>Frequency input ranges from 38Hz.to 1200Hz.

>Low power consumption

Mechanical:

>HN-GH12-1921Y motor

Software:

>PIC 16F877 Microprocessor.

> 20 MHz Crystal Clock

Section 2

General Installation Instructions

Getting Started:

After unpacking the Auto Tuner need to power it up. To do this you must first install the batteries. The Auto tuner takes Six AA batteries. The battery compartment is on the backside of your Auto tuner. Flip the unit over so the LCD screen is face down on a table. On the back of the unit you will see a removable door, this is where you will need to install the batteries. Remove the cover and insert batteries in the directions specified on the inside of the battery cover. After all of the batteries are installed, place the battery cover back on the unit and snap into place. You are now ready to use your newly purchased Auto tuner.

Tuning Strings:

To use the Auto Tuner to tune strings first you need to power it up. Pushing the on/off/enter button located on the right side just below the LCD screen turns the unit on. When the unit is powered up a welcome screen will appear saying Auto Tuner, this same screen will also tell you what version of software is loaded into your Auto Tuner. The current version of software is version 0.3. Check the Auto Tuner web sight for future accessories and latest software upgrades.

Auto Tuner can be found on the World Wide Web at:

www.vtc.edu/elm/projects/2002-2003/AutoTuner/WebPage/Title_Page

After the welcome screen flashes up for three seconds the menu screen will appear on the LCD. The menu screen asks you to choose between three different tunings offered by the current software version, standard, drop D or Eb tuning. For standard guitar tuning of 440Hz, Standard Tuning will appear on the LCD, to select it just hit the on/off/enter button. For special tunings such as drop D or Eb tuning hit the mode selection button to scroll through the different tunings. Each time you hit the button a new tuning will appear. To choose a tuning, hit the enter button to select it. Next select the string you want hold the unit to that tuning peg, pluck a string and then you’re on your way. It’s that easy.

The following steps are an example to tune a high E string in standard tuning.

Step 1:

Tune unit on

Step 2:

Scroll through the different tunings using mode selection button until you find standard tuning.

Step 3:

Select, standard tuning by pressing the enter button to the right of the mode selection button.

Step 4:

Move the string selection switch to the position of the high E

Step 5:

Hold Auto Tuner up to the tuning peg of the high E string as shown in figure 1.

Step 6:

Pluck high E string, print. A print out on the LCD screen will tell you if you are in tune. If string is out of tune, the motor will adjust string until it is in tune.

Figure 1

(Auto Tuner placement)

Warning: choosing different string on guitar than switch setting on unit can lead to damage and broken strings

Section 3

Theory of operation

Overview:

This section of the manual, theory of operation looks at the operations of the auto from the inside out. Concept drawings and descriptions that are provided will be divided up into three separate sections electrical, software and mechanical. First we are going to take a general look at the entire system overview.

Figure 2. Below shows the theory behind the entire system.

Figure 2.

System theory

The string on the guitar is plucked and the signal in feed through a ¼ “ jack or microphone found on later versions of the Auto Tuner. It is feed through a low pass filter to cut off frequencies above 2khz. This is to eliminate upper harmonics and noise that might interfere with the processing waveform. The range of frequency on a guitar range from 82.4hz, an open low E string and 329.6hz, for an open high E string. After the waveform is filtered, it is then feed through an lm339 comparator to convert the guitar wave into a square wave. This is done so the micro-controller can read the waveform.

The next step in this system process is done in software burned into the PIC 16F877 micro controller, which will be covered later in the software part of this section. The micro controller then compares the input signal against a value stored in its memory. If the string is to high then the micro controller sends a signal out, turning the motor in counter-clockwise (CCW), if the signal is to low, it turns the motor clock-wise (CW). The motor as it’s turning CW or CCW turns the tuning peg on the guitar. This whole process takes millisecond to execute, so in turn the signal is feed back through the system again until the micro controller can home in on the target frequency set by the six-position switch.

Electrical:

The general electrical functions of the unit are to filter, correct and display. All of these will be covered in this electrical section.

First is the electrical system layout of the Auto Tuner. Six AA batteries produce 9-volts of power for the motor is reduced to 5-volts by a To-7805 voltage regulated for the rest of the circuitry. The main circuitry can be found on two circuit boards connected by a 20-pin ribbon cable. The upper circuit board contains components that are for user input, such as the on/off button, mode selection button and six-position switch. These buttons and switch are for the user to navigate and communicate to the micro controller when using the unit. On\off button powers unit up and shut the unit down. The mode selection button allows the user to scroll through the different tunings. The six-position switch allows the user to select between the different strings. The upper circuit board also contains the low pass filter, lm-339 comparator to clean and convert in-coming waveforms and the A3968SA motor driver-chip for driving the motor. The Specs on these chips can be found in the appendices in the back of this users manual.

The bottom circuit board connected by the 20-pin ribbon cable is a programming board for the micro controller. This board also has the TO-7805 voltage regulated that steps the 9-volt battery supply to 5-volts. The 9-volts is to drive the motor only and not for the rest of the circuitry. The micro controller is the brain of the entire unit. This is where the software executes and corrects incoming signals. The micro controller used on this board is a PIC 16F877. The PIC has 8k of flash memory and 5 I\O ports. The pin out for the PIC, and a schematic for the programming board can be found in the appendices in the back of this manual. The last part of the electrical system is the LCD display. This is the menu and instructor to the user. The LCD used is a model DMC 16202N-LY-AME. This LCD runs off from 5-Volts. One of the features of this LCD is the backlight. Although this is a nice feature it increases the current draw considerably. This is why the LCD backlight turns off after three seconds, to save on battery life. The LCD can also be found in the appendices.

That is generally the electrical part of the system; the specs and pin outs can be found in the back of this manual. For a general electrical overview please refer to the electrical concept diagram in figure 3.

Figure 3.

Electrical Overview

Software:

The software of the system is the heart of the entire Auto Tuner. The software looks at in coming signals and decides on how to correct them. This can be seen in the figure 4. The signal is feed from the guitar then captured and check against a value in memory then corrected through the use of the motor. At the same time, the master clock is reset stopping the unit from shutting down and keeping the LCD on for only three seconds.

Figure 4.

The software also writes to the LCD, turns on and off its backlight. The software even takes input from the user and executes functions such as turning unit off and choosing the right tuning.

The software for the PIC micro controller is written in assembly language. This software is a special kind of assemble for use with PIC micro controllers and only has a 35 instructions in its set. These instructions are written in over 1500 lines commands that help the Auto Tuner to function.

Mechanical:

The mechanical parts of the Auto Tuner consist of the motor, gears, grippers and enclosure. A quick glance at the mechanical concept drawing in figure 5., will give you a general sense of where the parts are laid out in the enclosure. The 30-RPM gear motor runs on 9- volts and delivers about 31.3 oz\in’s of torque to equally sized spur gears. This is a 1:1 gear ratio. The reason for the two of the same gears is to not change the RPM or torque. The grippers are machined out of metal for durability and are mounted on a shaft that passes through the enclosure. The reasoning for two grippers is, ease of placement on guitars having tuning pegs on both sides of their headstock.